( is usually acquired from detector using...)Practical Aspects of Evaluation of Chromatographic Data in Size Exclusion Chromatography

is usually acquired from detector using A/D converter. To avoid viscosity effects, the lovest detectable sample concentrations are preferable, thus the signal measured is usually low. The range for dataacquisition should thus be selected to use all the board resolution. On some types of detectors, the scaleable recorder output could give better signal/noise ratio than the integrator output. The peaks are usually wide, thus data acqusition frequency can be set to the minimum.

Integration
Peak width and threshold definition are the base parameters for the integration algorithm to locate the peak starts and end. In standard chromatography, the peak width of the narrowest peak of interest is recommended as starting point. For wide polymer peaks, it can lead to some signal deformation and information loss. The peak width of the low molecular markers should be used instead. The peak width parameter also defines, how many points from the original data will be used functioning like a some kind of a filter. As its setings will influence the determined retention times to some extent, it is essentiall to use the same value for integration of narrow standand peaks and wide unknown polymer peaks. The threshold parameter together with the peak with determines where the peak starts and ends will be located. The value equal twice baseline noise is a good starting point.

Major source of errors and ambiquities in GPC evaluation is the determination of the peak start and ends and the baseline setting. Especialy the Mn (number average) values are extremely sensitive to peak end detection and the type of baseline separation (baseline versus valey to valey). Similarly, the M(z+1) and Mz averages are sensitive to the peak start definition. High quality instrumentation and columns are the necessary prerequisite for correct interpretation of tailing peaks the peak tail can be either low molecular polymer or instrument
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